1. Field of the Invention
The present invention relates to a method for fabricating a flexible semiconductor electrode. More particularly, the present invention relates to a method of fabricating a flexible semiconductor electrode that includes transferring a semiconductor electrode from a first substrate to a flexible second substrate having an adhesive layer using both pressure and heat. Also, the present invention is directed to a flexible semiconductor electrode fabricated by the method, and a solar cell employing the flexible semiconductor electrode.
2. Description of the Related Art
A solar cell, which is a photovoltaic device for converting sunlight into electrical energy, uses energy that is unlimited and environmentally friendly, unlike many other energy sources, and has become increasingly more important over time.
Monocrystalline and polycrystalline silicon-based solar cells are more prevalent than other types of solar cells. However, silicon-based solar cells can suffer from high production costs and low photoelectric conversion efficiencies.
One alternative to silicon-based solar cells is an organic material-based solar cell that can be produced at low cost. In particular, significant attention is being paid to dye-sensitized solar cells because of their low production costs. Dye-sensitized solar cells, one kind of photoelectrochemical solar cell, utilize photo-sensitization of metal oxide semiconductors. The cells have a simple structure that generally includes a semiconductor electrode made from dye-absorbed, highly porous, metal oxide nanoparticles deposited on a transparent electrically conducting substrate, and a counter electrode, with an electrolyte interposed therebetween. The semiconductor electrode includes an electrically conductive transparent substrate, a metal oxide, and a light absorbing layer.
Functioning to extract energy from light, a dye-sensitized solar cell is a photoelectrochemical solar cell in which a photosensitive dye molecule is chemically adsorbed on a semiconductor material having a wide energy band gap. The photosensitive dye molecule functions to absorb visible light to produce electron-hole pairs. In addition to being environmentally friendly and being fabricated in a transparent form, dye-sensitized solar cells have advantages over silicon-based solar cells or chemical semiconductor-based solar cells in terms of production cost, and over other organic material-based solar cells in terms of photoelectric conversion efficiency.
A flexible dye-sensitized solar cell, employing a flexible semiconductor electrode, has attracted significant attention owing to its ability to be used as part of an auto-chargeable battery for mobile phones and next-generation personal computers (PCs), such as wearable PCs, and to its ability to be mounted on numerous items, such as clothes, caps, automobile glass, buildings, and the like.
Flexible semiconductor electrodes generally should be manufactured at 150° C. or less because flexible substrates are very likely to distort at higher temperatures.
Methods for manufacturing flexible semiconductor electrodes include printing a paste, which is baked at a low temperature, on a flexible substrate and drying it at less than 100° C., or forming a semiconductor layer on an opaque metal foil. However, the solar cells fabricated through such methods suffer from problems of low photoelectric conversion efficiency and poor film stability. Therefore, there is a need for a novel method for manufacturing a flexible semiconductor electrode at low temperatures in a stable manner.
According to one such method, a porous layer is first formed on the surface of a first substrate, followed by the formation of a semiconductor layer on the porous layer using liquid-phase epitaxy. A second substrate is attached to the semiconductor layer, and the first substrate is separated from the semiconductor layer using the porous layer, which results in the transfer of the semiconductor layer from the first substrate to the second substrate. In this method, the transfer of the semiconductor layer to the second substrate by the exertion of physical force on the porous layer requires strong adhesion between the semiconductor layer and the second substrate. Unfortunately, this causes some of the porous layer to remain on the semiconductor layer.